Table of contents

A highly efficient parametric generator of near-infrared radiation was constructed. An unfocused hyper-Gaussian neodymium laser beam was used to pump ADP crystals grown by a new fast method. The output energy was several joules.

An analysis is made of the problems encountered in controlled nonlinear modification and stabilization of picosecond pulses of the fundamental and higher-order TE and TM modes traveling in fiber-optic waveguides. The sensitivity of such processes to initial amplitude-phase characteristics of signals, waveguide geometry, and propagation mode is the reason for the great diversity of the energy and spatial tuning scales. The advantages and shortcomings of soliton and nonsoliton mode signals in waveguides are considered. A review is given of near-threshold regimes for the stabilization of nonsoliton pulses and of some of their parameters over finite distances in graded-index waveguides. Data-handling capabilities of nonlinear communication channels, governed by the transmission distance and channel geometry, are discussed.

A study was made of a high-power high-pressure electron-beam-controlled laser utilizing the 5d-6p and 7p-7s transitions of the Xe atom and having an active volume of 9 liters. The dependences were obtained of the electrical parameters of an electron-beam-controlled discharge and of the energy parameters and spectral composition of the output radiation on the type of buffer gas, the discharge circuit parameters, and the composition and pressure of the active mixture. When the medium was pumped by an electron beam alone, having a current density of ~ 6 A/cm² and a pulse duration of O.7 μsec, the laser output energy was ~ 6/J (efficiency ~ 1.5%), but for electronbeam- controlled pumping it was roughly 20 J. The physical lasing efficiency, in terms of the electric field, was ~5%. An analysis was made of the mechanism of the establishment of the active medium conductivity and of the population kinetics of the active transition levels.

A theoretical investigation is made of the transient regime of stimulated enthalpy scattering of light by ultrasound in iodine lasers. The distinguishing characteristics of such scattering are identified. A comparative analysis is made of the stability of working mixtures of iodine lasers under conditions of stimulated enthalpy scattering and ways of verifying experimentally the theoretical results are considered.

An experimental investigation was made of the characteristics of a photodissociation laser operating on the B–X (353 nm) and C–A (485 nm) transitions of the excimer XeF. The laser was pumped with vacuum ultraviolet radiation from an open high-current discharge. The energy in a laser pulse and the average specific output energy reached values of respectively 28 J and 18 J/liter at 353 nm and 14.5 J and 10 J/liter at 485nm. Measurements were made of the instantaneous lasing efficiency, defined as the ratio of the laser output power to the electrical input power from the pump source. At the maximum of a laser pulse the efficiency reached 0.8% at 353 nm and 1 % at 485 nm (corrected for the geometrical utilization factor of the pump source radiation). It was established that the pump source efficiency was 7.5–8.5% and that the quantum efficiency of the formation of XeF(B) averaged over the pump band was 85 ± 5%. Ways of raising the laser efficiency to ~ 2% were considered.

An experimental investigation was made of lasing of an optical-breakdown plasma in an He–Xe gas mixture exposed to CO₂ laser radiation. A wide range of pump pulse energies and durations and active mixture pressures was used. Lasing was realized on four Xe I transitions (λ = 2.03, 2.65,3.4, and 3.65μ). The pump pulse duration was found to exert a strong influence on the lasing characteristics of the optical breakdown plasma. An analysis was made of the role of gasdynamic processes in the interaction of the CO₂ laser radiation with the gas close to a target during the buildup of inversion. A quasi-cw lasing regime of the recombination laser in the optical breakdown plasma was observed.

Attention is drawn to a close analogy between lasers and stimulated generation of a Bose condensate of Cooper pairs in a superconductor. The same analogy should apply also to the processes associated with phase transitions in the expanding universe. On the basis of this analogy we can postulate a complex dynamics of the processes that have occurred during the earlier stages of the evolution of the universe. In particular, we can expect regimes which are described by a strange attractor.

A new form of a quasisteady level distribution of vibrationally excited molecules is found under pumping conditions. Characteristic features of a quasisteady distribution in a gas containing CO₂ molecules are considered.

A theoretical investigation is made of the radial motion of atoms in a beam decelerated by an opposite optical beam. It is shown that when the transverse size ρ of the laser beam is much greater than a certain critical value ρ_cr, then the interaction causes chiefly diffusion broadening of the atomic beam. If the laser beam radius is less than or of the order of ρ_cr, then monotonic diffusion broadening of the atomic beam is accompanied by oscillations due to the focusing effect of the laser beam.

Mechanisms of thermooptic distortions in active elements, which are important in the case of athermal glasses, are investigated theoretically for the first time. Detailed studies are made of the deformation of the end surfaces of active elements of rectangular and circular cross sections subject to an allowance for the specific pumping conditions near the ends. A numerical modeling allowing for thermooptic distortions and large-scale focusing is reported: it reveals characteristics of the divergence of high-power laser radiation in an amplifier with an active element of rectangular cross section.

A theoretical investigation is made of the characteristics of wavefront reversal in the course of a degenerate four-wave interaction in moving slow-response media. It is shown that the displacement (by a moving medium) of amplitude and phase gratings, and also diffusion of excited particles may influence greatly the parameters of a reversed wave. The characteristics of a nonlinear mechanism of light-induced heat evolution in thermodynamic-nonequilibrium media are determined for spatially inhomogeneous radiation.

A study of resonant interaction of He–Ne laser radiation with the 3s₂–2p₄ neon transition (of 0.63 μ wavelength) and with the vibrational-rotational F₂⁽²⁾methane transition [P(7) line of the ν₃ band at 3.39 μ] revealed narrow magnetooptic resonances due to the nonlinear Faraday effect. An analysis was made of the dependences of magnetooptic spectral structures of this type on the angular momenta of the energy levels and on disorienting collisions in the gas. It was established that the method of recording the nonlinear magnetooptic resonances resulting from the Faraday rotation had a higher sensitivity than the normal method of measuring magnetooptic absorption resonances.

The first results are given of investigations of frequency resonances of a ³He–²⁰Ne/¹²⁷I₂ laser (0.63 μ wavelength) emitting two modes with parallel polarizations. Investigations were made of the resolution, of the amplitudes of the frequency resonances and their shifts, and of the influence of the temperature on the frequency pedestal. It is shown that the high signal-to-noise ratio makes frequency resonances promising for use in laser spectroscopy.

An analysis is made of the process of propagation of radiation in unperturbed and perturbed multilayer optical waveguides. A dispersion relationship convenient for the calculation of the characteristics of complex waveguide structures is derived. A determination is made of the parameter representing the degree of localization of the optical flux of a mode in the vicinity of a given interface between media forming a waveguide. A study is made of the maximalization of the light flux of a mode in the region of a perturbed boundary of a waveguide. Relationships are obtained for calculations dealing with the processes of emission, reflection, and transformation of modes in sections of multilayer waveguides perturbed by corrugations. The influence of an asymmetry of corrugations on the process of mode diffraction is determined. Conditions are found for the use of corrugated sections of optical waveguides in the construction of nonreciprocal integrated- optics components.

An analysis is made of the problem of mode propagation along flat and corrugated surface optical waveguides. The dispersion relationships are derived for multilayer surface waveguides. Characteristics of mode attenuation during propagation along corrugated sections of waveguides are considered, as well as the problems of increasing the efficiency of mode conversion into leaky waves, generation of surface electromagnetic waves, and influence of the absorption of light in a metal on the propagation and conversion of surface optical waves.

Resolved vibrational-rotational spectra of nitrogen excited by a high-current pulsed discharge were recorded. The rotational and vibrational population distribution functions were determined for various time delays. The rate constant of the elementary vibrational-vibrational exchange process was determined: K₁₀⁰¹ = (1.5 ± 0.6)× 10⁻¹³ cm³/sec.

The rate constant for vibrational-vibrational exchange, K₁₀⁰¹ = (1 ± 0.4) × 10⁻¹³ cm³/sec, was determined under conditions of selective biharmonic excitation of the first vibrational state of nitrogen. Procedural aspects of measurements of the vibrational relaxation time under biharmonic excitation conditions are discussed.

It has been established that the optical breakdown threshold of glasses W_th is related to the Landau-Placzek ratio R_LP of the scattered-light spectrum. Published data and the results of measurements of the scattered-light spectra are used to obtain dependences of the relative optical breakdown threshold W_th on R_LP for various Soviet and foreign glasses. It is found that W_th decreases as R_LP increases. It is suggested that the role played by chemical and structural inhomogeneities in damage to glasses by high-power laser pulses should be taken into account. It is proposed that results of scattered-light spectroscopy should be used to search for glasses having high W_th.

A theoretical analysis is made of the operation of a Fabry–Perot interferometer containing a nonlinear (cubic) medium. An instability of the operation of this interferometer in the presence of perturbations traveling at an angle to exciting plane waves appears at lower amplitudes than those necessary for the appearance of a hysteresis.

It is shown that a ring laser with a second-harmonic generator can double the number of stable states, resulting in self-modulation of the radiation. The system is described by a one-dimensional mapping that can be used to trace analytically the transition to stochasticity and to make universal calculations of those values of the bifurcation parameter at which the character of the self-modulation changes.

A high-power singly resonant LiIO₃ crystal optical parametric oscillator (OPO) was developed for selective excitation of organic macromolecules. By using a high-Q resonator for λ = 1.3–1.7 μ and a large (~ 9 mm) pump beam diameter, a useful radiation energy higher than 0.1 J was obtained in the λ = 2.5–3.2 μ range in spite of the appreciable absorption of the crystal in this range. The results indicated that it would not be advisable to use crystals longer than 4 cm in the proposed system in view of mode locking and stimulated Raman scattering of resonant radiation from polaritons. An experimental investigation was made of the resonant effects of OPO radiation on OH group bonds in cellulose nitrate molecules.

It is shown that the increment describing formation of a periodic structure on the surface of mercury by laser radiation under the conditions in the experiments of Keilmann [Phys. Rev. Lett. 51, 2097 (1983)] is governed by the evaporation pressure p. Similar experiments involving measurement of p can give new information on the kinetics of a nonequilibrium phase transition and on the optical and thermophysical characteristics of matter in a superheated metastable state.

A high-sensitivity pulsed CARS (coherent anti-Stokes Raman scattering) spectrometer with a resolution of 3 × 10⁻³ cm⁻¹ is described. Spectra with a resolved rotational structure of the Q branch of the v₁ vibrations of ³²SF₆ and ³⁴SF₆ molecules were obtained. Measurements were made of the vibrational-rotational interaction constant α and of the vibrational frequency v₁.

It was found experimentally and theoretically that the hydrodynamic acceleration mechanism and also dielectronic recombination in the heating phase and three-body recombination in the expansion phase are well explained by the experimentally observed energy spectra of ions in an expanding laser plasma.

The first experimental investigation was made of the vibrational-rotational emission spectrum of a high-power electron-beam-controlled cw CO laser with cryogenic cooling of the working mixture and a nonselective three-pass telescopic resonator. Lasing on 24 vibrational-rotational lines was observed. Variation of the composition and temperature of the laser mixture resulted in different distributions of the power over the emission spectrum of the laser. The maximum efficiency of the emission of one vibrational-rotational line at an initial laser mixture temperature of ~100 K was ~4.5%.

Determination was made of the spectral characteristics of two-section injection lasers with a coupled resonator (also known as a coupled cleaved cavity or C³). The process of frequency tuning by variation of the injection current in the controlled section of the laser was studied. When frequency was modulated by a microwave current, the mode switching time was less than 100 psec.

An experimental investigation was made of the luminescence and microwave conductivity of K8 and ZhS 11 optical glasses under conditions of subthreshold irradiation by a quasi-cw neodymium laser. For ZhS 11 glass it was established that the luminescence depended on temperature and the influence of photostimulation was observed at the 1.06 μ wavelength. The activation energies of the microwave conduction and subthreshold luminescence processes were determined for ZhS 11 glass.

A system for three-photon Doppler-free excitation of two-level atoms is proposed. It is shown that this is equivalent to the excitation of a two-level system with an effective interaction Hamiltonian. An analysis is made of a system for selecting the detuning of the excitation frequencies that can completely compensate for Doppler broadening. Numerical estimates are made and these show that even for small isotope shifts and high temperatures of the excited gas, excitation having a high probability and a high isotopic selectivity can be achieved.

Plasma sheets formed by a creeping discharge on the surface of an insulator were used as a preionization source and as electrodes in atmospheric-pressure CO₂ lasers with a cross section of the active medium channel amounting to 150 × 150 mm. The output energy parameters of such lasers were not inferior to those of lasers with electron-beam preionization.

An experiment was carried out in which a method suggested earlier by the present authors was used to investigate the transverse mode composition of multimode coherent light beams. A study was made of multimode beams in a graded-index waveguide excited by a Gaussian beam. The experimental dependences of the coefficients describing the excitation of four modes on the Gaussian beam radius were in agreement with the theory.

Stimulated Raman scattering in compressed hydrogen pumped with picosecond YAG:Nd laser pulses was used to generate radiation of wavelengths 1.907 and 9.191 μ. The average energy of the pulses represented by the first and second Stokes components of stimulated Raman scattering was 34 mJ and 230 μJ, respectively.

It has been established that the contribution made by vibrational excitation may be appreciable, particularly in the case of molecular polarizabilities, and should be taken into account when determining the temperature and density in nonequilibrium gases. The results are calculated for important molecules such as CO, CO₂ and SF₆.

Low-loss fiber waveguides with ultraviolet-solidified polymer coatings were fabricated. A study was made of the influence of temperature and of ultraviolet radiation on the losses in these waveguides. The mechanical strength was also determined.

A study was made of the strength of welded joints formed between fiber waveguides made of quartz glass and intended for optical communication systems. An electric arc was used in welding. The use of chemical methods for the removal of the protective layers in the preparation of the fiber ends and etching of the surface layer of the waveguide increased the strength by a factor of 7.5. The welding technology developed for this purpose made it possible to form welded joints with an average breaking strength of 18 N.

A semiclassical method is used to study cooperative spontaneous radiation (superradiance) emitted from an excited medium in a thin dielectric waveguide subject to an allowance for the highest-Q normal wave in the waveguide (constant profile fields). A radiation pulse is described by a nonlinear equation which represents weakening of the interaction between matter and a field of constant profile in the case of a large-area pulse. This results in partial utilization of the stored energy, reduces the steepness of the edges of a pulse and its maximum intensity, and suppresses oscillation replicas.

An experimental investigation was made of a CO chemical laser utilizing a CS₂–N₂O–O₂ flame having an active medium up to 3 m long. Attention is drawn to the need to match the dimensions of the active medium to the mode structure of the resonator. A chemical efficiency of 15% was achieved for a cw laser radiation power of around 100 W.

An analytic expression is obtained for the threshold of a semiconductor laser in the form of a five-layer structure with separate electron and optical confinement. An analysis is made of the dependence of the lasing threshold on the thickness of the active and waveguide layers, and also on the permittivities of these layers.

An experimental investigation was made of guiding channels in optical waveguides made of glassy chalcogenide semiconductors. The results were used to propose a multichannel optical fiber system for the infrared range in which polarization of the transmitted radiation would be conserved. It was found to be possible to construct guiding channels with different values of the birefringence and their potential applications were considered.

The angular divergence of helium-neon laser radiation was found to depend on variation of the emission frequency within the limits of the gain profile of the active medium. The maximum relative change in the angular divergence was 4 ± 2%. This change appeared because of a nonlinear frequency dependence of the refractive index of the active medium in the region of the Doppler-broadened gain profile. The effect appeared particularly clear in the case of long optical paths.